Spinal fusions are indicated where a natural spinal deformation has occurred, where there has been damage to intervertebral disks, or where fracture of a vertebra has occurred. One method for fixing vertebrae relative to each other is disclosed in copending patent application Ser. No. 08/075,239, filed Jun. 10, 1993 now U.S. Pat. No. 5,470,333. With the fixation device disclosed therein, one or two plates are secured to the sacrum and a single rod extends from the sacral plates superiorly along the saggital plane posterior to the spine. Transverse bars are rigidly secured to the rod at a location posterior to the vertebra to be fixed. The lateral extensions of these transverse bars are secured bilaterally by screws to the pedicles of the vertebra to be immobilized during the fusion process.
For some deformations and injuries, application of a spinal plate with a superiorly extending rail with transverse bars and pedicle screws are not required. Another method suggested by Magerl for fixation of successive vertebrae is to use translaminar screws. Conventionally, these translaminar screws extend through the spinous process and then through the lamina at the facet joint into and through the pedicle of the successively inferior vertebrae. Oftentimes a deformity and/or injury requires a laminectomy to eliminate nerve root compression, such as occurs with degenerative spondylolisthesis. When a laminectomy is required, the spinous process and the underlying lamina are removed. When the spinous process is removed, translaminar screw fixation is not generally adequate to stabilize successive vertebrae pending healing of the spinal fusion. This is because the lamina of the superior vertebra is generally relatively weak, especially where a laminectomy has been performed. Because the lamina is relatively weak, the translaminar screws can toggle relative to the superior vertebra, causing breakage in the lamina around the screw and destabilization of the joint. Thus, where a laminectomy has been performed, use of a sacral/rod/pedicle fixation system, such as that described above, is normally required.